1. Another Example
iSENSOR S0 S1 S2
iEXT
/iSENSOR•iRET
oCYL=1
oCYL=0

2. Example #2 State Diagram
iSENSOR S0 S1 S2
iEXT
/iSENSOR•iRET
oCYL=1
oCYL=0
cS0 = cS2•/iSENSOR•iRET + cS0•/iSENSOR + /cS0•/cS1•/cS2
cS1 = cS0•iSENSOR + cS1•/iEXT
cS2 = cS1•iEXT + cS2•/(/iSENSOR•iRET)
= cS1•iEXT + cS2•(iSENSOR + /iRET)

3. Ex #2 - RLL-Plus Stages S0 S2 S1 oCYL=0 /iSENSOR•iRET iSENSOR iEXT

4. State Machines in Ladder Logic
Pure relay logic - traditional design:
2 states = 1 coil
3-4 states = 2 coils
5-8 states = 3 coils, etc.
difficult to debug, modify and document
Pure relay logic - “one-hot” design
1 coil per state
easier to debug, modify, and document
RLL-Plus
“Stages”
JMP “coils”
easiest to write and maintain
not available in all brands of PLC’s

5. Multi-state Example
When sensor detects block; clamp block, drill hole, shift, drill 2nd hole, shift back, release clamp

6. Inputs and Outputs iSENSOR block present iDRILLDN drill is down
iDRILLUP drill is up
iCLAMPED fully clamped
iRELEASED fully unclamped
iPOS1 unshifted
iPOS2 shifted
oDRILL start drilling
oCLAMP activate clamp
oSHIFT shift block holder

7. State Diagrams
One state per “action”
Look for “wait” states needed

8. State Diagram

9. RLL-Plus

10. RLL-Plus

11. RLL-Plus